Oh wow, I really like Nymphaea! I've never heard this term before, so I wouldn't have guessed it's the Latin name for a flower (it looks more like Latinized Greek to me, though). It reminds me a bit of Nimue, in terms of sound.
Of your combos, I like:
Nymphaea Catherine
Nymphaea Hester
Nymphaea Tess
Nymphaea Pearl
I would also propose:
Nymphaea Lauren
Nymphaea Laurel
Nymphaea Caroline
Nymphaea Lydia
Nymphaea Brooke
Nymphaea Clare
Nymphaea Jade
Nymphaea Jane
Nymphaea Joy
Nymphaea Joyce
Nymphaea Lynette
Nymphaea Lynne
Nymphaea Lysette
Nymphaea Rhoda
Nymphaea Rhode
Nymphaea Romilly
Nymphaea Rose
Nymphaea Sylvie
Nymphaea Vesper
Nymphaea Velia
Nymphaea Wren
Nymphaea Xanthe
Nymphaea Heather
Nymphaea Hope
Nymphaea Zelma
Nymphaea Calypso
Nymphaea Larue
Nymphaea Lux
Nymphaea Magdala
Nymphaea Magdalen / Nymphaea Magdalene
Nymphaea Melusine
Nymphaea Penrose
Nymphaea Tara
Nymphaea Terra
Nymphaea Thessaly
Nymphaea Topaz
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